my 94 ford f150 5.0 will occasionally pop or sputter (misfire)and loses power for no reason? And then it will suddenly"catch" and accelerate. I have tried to recall the circumstance at each occurance, and I think it happens more when fuel tank is 1/4 or less. (could be coincidence)I filled it tonigt and took a drive, no problems. veh. has 80,000 + miles.

From your description and from the description only, I would venture a guess that maybe the fuel sending unit is faulty and giving a bad reading to the gauge. So, without having it to check, I would just be sure it has over 1/4 tank. When it starts sputtering and you fill it up, how many gallons does it take?

This truck has 2 tanks, when I fill the tank or tanks they seem to take the amount of fuel they should. I should have mentioned that the last occurence was a heavy rain day, I dont recall if the other times were. I switched to the rear tank which was 3/4 full and the problem continued. I am guessing at wires or water in the tank(s) I did add a bottle of "Heet" as well as a bottle of concentrated injector cleaner to both tanks. I will be changing plugs,wires,cap and fuel filter on saturday.

Well, went through whole tuneup procedure, changed plugs, cap, wires, plugs, fuel filter, timing etc. the problem persists. Not really sure how to check the fuel for water? Thinking of syphoning some out of tank into clear bottle and see if it seperates? Does water float on top of gasoline?

This is the second engine in this vehicle,(long before I purchased it) I wired it from specs on a 1994 5.0 litre, is there a way to find out what year my engine actually is? where would I find a serial number or code on the engine? Has the firing sequence changed model year to model year?